The invention is based on a speed governing system for an internal combustion engine with self-ignition as generally defined hereinafter. A system of this kind is known from German laid-open patent application DE-OS No. 31 30 080, which relates to a Diesel idling governor.
Diesel engines have a number of properties that differ from those of gasoline engines. Vehicles with Diesel engines therefore perform differently in some respects as compared with vehicles having carburetor or injection engines. For instance, if the driver suddenly lets up on the accelerator pedal, the speed or rpm of the engine drops relatively rapidly. The effect of this sudden let up on the pedal is an abrupt deceleration of the engine. Letting up on the pedal immediately after cold starting causes an even more severe speed drop. After the pedal has been released, the engine must be regulated to idling with the aid of an idling governor. Diesel engines with a high number of cylinders--six or more--present the associated idling governor with a steep drop in rpm in the case of abrupt deceleration, that is, letting up on the pedal, immediately after cold starting, because of the greater friction in the engine at that time. The danger therefore exists that the engine speed may be undercut to an impermissible extent, speed undercutting, for example, which can cause stalling.
After starting, in the cold phase, misfiring can occur which causes a drop in engine speed. The idling governor reacts to an rpm drop immediately by raising the rpm. A series of misfirings, especially in the cold phase, is therefore capable of causing very rough engine operation.
With the idling governors known previously, an optimal governing quality was not attainable. Known idling governors could not distinguish between the problem of quickly intercepting the engine speed drop in the case of abrupt deceleration, and that of not to misfiring. These two mutually contradictory requirements demanded that a compromise be made, but such a compromise was heretofore unattainable. Because of the parameters involved, the events described above instead lead to overcompensation, especially in the case of misfiring.